1. Field of the Invention
The invention relates to a device for producing a plurality of individual composites having two or more layers. The composites are made from a plurality of plastic film webs which are sealed together. The invention also relates to a process for producing a number of individual composites having two or more layers. The layers are made from plastic film webs including one or more biaxially stretched thermoplastic, stretched thermoplastic, and monoaxially unstretched thermoplastic, coextruded films. The films are provided with a sealing layer on at least one side, and the composite is formed by sealing with the application of pressure and heat.
2. Background
Various industries such as apparatus engineering, automotive and aeronautical engineering, or safety technology, are becoming increasingly interested in high-strength film composites and composite bodies in the form of webs, semi-finished products such as sheet and finished components. Because of this interest, techniques for producing mechanically relatively high-strength products are being developed by sheet manufacturers. Simultaneously with the modification of polymeric materials used in sheet production by the incorporation of reinforcing materials such as textile, glass or carbon fibers, techniques are being developed for manufacturing inherently strengthened sheets using orientation techniques.
These techniques include roll-press stretching or the process disclosed in EP-A 0,207,047, the essential processing technique of which consists of pressing a multiplicity of biaxially stretched films treated with thin coextruded sealing layers under the application of pressure and heat to form a homogeneous sheet of any desired thickness. The stack of films inserted between two press plates thus is typically introduced into batch-operation, hydraulic platen presses of single or multi-platen design. The pressing operation is governed by process parameters such as pressure, temperature and time. The process parameter of time, in particular, hinders economical production of composite laminates, especially when through-heating very thick sheets. Continuously operating presses such as double-belt presses represent a practical, time-saving solution in this regard, but only have limited use due to the speeds they can achieve.
German Patent 35 30 309 discloses a process and a device for the continuous production of thermoplastic webs and for further processing to sheets or films, from at least one extruded thermoplastic web, which is heated to processing temperature, and then cooled while in the heated state between two pressurized stationary plates. During this process, the surface of the thermoplastic web is sized and smoothed. The cooling of the thermoplastic web takes place under the effect of surface pressure where it is guided, during cooling, between two continuously moving, endlessly circulating press belts.
A uniform surface pressure is exerted from the plates hydraulically or mechanically onto the inner side of the moving press belts and transmitted from these to the thermoplastic web. The plates are held at a temperature lower than the final temperature of the thermoplastic web in order to maintain a temperature gradient between the thermoplastic web, press belt and plate.
Cooling of the thermoplastic web takes place by dissipation of heat from the web via the press belt to the plates by thermal conduction. Also, the surface pressure is exerted continuously throughout the duration of cooling the thermoplastic web between the press belts.